What is an appropriate age for kids to take swimming lessons?
I have received conflicting advice from my friends so I am posting here.

Our will be 18 months old this month. He loves water. He used to have chronic ear infections when he was a baby. He has ear tubes. We use ear plugs when he takes bath.

We live in MN where winters are brutal and we are always looking for new things to do. I think he will enjoy swimming. We have found a school near our home. I have not talked to them yet.

What kind of diapers are required?
Do we need special ear plugs for swimming?
Are there any precautions we should take to make it safe and enjoyable.